This invention relates to a color compensation method to obtain optimal conditions for exposure in photographic printers and, more particularly, in color printers, to a color compensation method for adjusting the amount of light which often fluctuates due to differences in the type of color negative films, individual printers and/or picture frames.
In order to print color photographs of high quality, it is necessary to optimally control conditions for development of negative films, conditions for exposure by printers and conditions for development on photographic paper. The amount of light from a light source of a color printer is automatically adjusted by means of cyan (C), magenta (M) and yellow (Y) filters in a color compensation filter type device in the following procedure. The amounts of light for three primary colors obtained when no color compensation filter is inserted in an optical path are measured by photosensors such as photodiodes. The measured values are represented by the letters RI, GI and BI and the target values for R (Red), G (Green) and B (Blue) are represented by the letters Ri, Gi and Bi as shown in FIG. 1. For instance, in the color red R, the target value is attained by decreasing the amount of light by (RI-Ri) with a C-filter. The amounts of light for green G and blue B are also adjusted by inserting an M-filter and a Y-filter to respectively decrease the amounts of light by (GI-Gi) and (BI-Bi) in a manner similar to the above.
Colors are controlled in amounts needed to achieve desired values. If it is assumed that, as shown in FIG. 1, the difference (RI-Ri) between the desired amount of red light and the amount of light actually received from a light source is smaller than the differences (GI-Gi) and (BI-Bi) of green and blue light, the amount of light A=RI-Ri is attenuated for all colors or, in other words, wasted. If the amount of light from the light source is initially set at a low value in order to avoid this waste, such an operation may cause the light amount to be insufficient when the lamps deteriorate or when the power source voltage fluctuates.